Cable drawworks mechanisms have been used in drilling rigs for decades. Cable drawworks are, typically, motor-driven drums used to reel in or pay out a cable used on the drilling rig to raise or lower a traveling block within the rig. The cable will typically be used with pulleys and pulley blocks attached to the top of the rig and the traveling block, respectively. The traveling block is used for tripping pipe in and out a drill string, as well known to those skilled in the art. Various methods and devices have been developed for this purpose.
U.S. Pat. No. 2,505,088 issued to Athy teaches the use of two cable drums attached to either end of the cable coupled to a traveling block within a drilling rig through a series of pulleys. Having two drums doubles the speed that the cable can be reeled in or paid out resulting in doubling the speed that the traveling block can be raised or lowered within the drilling rig. The disadvantage of such a device is that two cable drums are required for this which increases the amount of space needed for the drums. Furthermore, additional drive train components are required for applying power from a motor to turn the two drums.
U.S. Pat. No. 4,438,904 issued to White teaches a drawworks mechanism that comprises a number of intermediary shafts having clutches that may engage or disengage power from an input drive shaft to the intermediary shaft. The mechanism consists of a number of chain and sprocket drive means for coupling rotation of power from one shaft to another. The disadvantage of this system is the physical space required to house such a mechanism on a drilling rig platform.
U.S. Pat. No. 6,182,945 issued to Dyer et al. teaches a complex drawworks mechanism comprising the use of redundant motors and gear transmissions for applying power to the cable drum. The disadvantage of this system is the significant size of the mechanism which necessitates that the mechanism be located apart and away from the drilling platform.
It is, therefore, desirable to have a drawworks mechanism that is compact enough so that it may be located directly on a drilling platform yet having sufficient power and braking ability to safely reel in and pay out cable for raising and lowering a traveling block within a drilling rig.